It is known for microcontrollers and the like to be used to drive, by way of example, switch mode power supplies, resonant converters, induction heaters, etc, whereby the microcontroller is required to generate a high frequency modulated signal waveform, for example in the region of 150 to 1000 kHz. Such modulated waveform signals are required to comprise a precise frequency resolution, for example in the range of 11 to 14 bits. In addition, suitable microcontrollers are typically required to be highly integrated, in order to provide reliable and low-cost solutions, whilst also being flexible in their operation and architecture.
In order to keep both costs and power consumption down to acceptable levels, semiconductor devices comprising microcontrollers are often required to utilise slower operating clock speeds, and slower, less expensive components. However, a problem with existing microcontroller architectures is that such restrictions on the operating clock speeds have the detrimental effect on the microcontrollers in that they are incapable of generating modulated signal waveforms comprising high enough frequencies, whilst also providing high enough frequency resolution for minimizing output voltage ripple and, thus, also noise levels, as required for switched mode power supplies utilized in the telecommunication industry, where designers must respect regulations of the International Telecommunication Union standard ITU-T O.41 and specifically the standard for Psophometric Noise For Use On Telephony-Type Circuits' tests.
Typically, current on-chip timers and PWM (Pulse Width Modulation) modules are able to achieve a maximum frequency resolution of less than 10 bits, for a 100 kHz waveform. As will be appreciated, for existing applications where a frequency resolution of 11 to 14 bits is required for up to a 1000 kHz waveform, these current on-chip timers and PWM modules are inadequate.
In order to overcome this problem, whilst maintaining costs and power consumption down to acceptable levels, it is known for on-chip timers and PWM modules to be operably coupled to an external digital to analogue converter (DAC) and voltage controlled oscillator (VCO). FIG. 1 illustrates an example of such a known solution comprising a microcontroller to generate a high frequency modulated waveform signal comprising a high resolution. The semiconductor device 100 comprises an on-chip timer 110 arranged to generate a modulated waveform signal.
As previously mentioned, in order to keep costs and power consumption down to an acceptable level, semiconductor devices (microcontrollers) are required to utilise slower operating clock speeds, and slower, less expensive components. Accordingly, the timer 110 is capable of generating, say, a ‘coarse’ 100 kHz modulated waveform (MWrough) comprising a resolution of less than 10 bits. The coarse modulated waveform (MWrough) is then provided to an external digital to (MWrough) analogue converter (DAC) 120 and voltage controlled oscillator (VCO) 130. In this manner, the external DAC 120 and VCO 130 are able to refine the coarse modulated waveform (MWrough) into high-frequency modulated waveform (MWfine) of, say, up to 1000 kHz comprising a resolution of 11 to 14 bits.
A problem with this known solution is that there is a need to use external components to refine the on-chip generated modulated waveform. The resolution of the high-frequency generated waveform (MWfine) is generally equal to the resolution of the timer modulated waveform (MWrough). The higher resolution of the modulated waveform (MWfine) may be achieved by lowering the frequency of the timer generated coarse modulated waveform (MWrough), which increases the resolution thereof. The frequency level of the coarse modulated waveform (MWrough) determines smoothing factors of the external digital-to-analogue converter (DAC) and voltage controlled oscillator (VCO); the higher the smoothing factor the longer the settling time and slower dynamic response of the system. Thus, the chain of components and the characteristics of such a semiconductor device result in reduced reliability, increased system costs and worse dynamic response in comparison to fully integrated systems.